1. Field of the Invention
The present invention relates to a pigment preparation with metal effect pigments, wherein the pigment preparation contains metal effect pigments the average size d50 of which lies in a range of from 1.7 to 2.8 μm and the average thickness h50 of which lies in a range of from 15 to 50 nm, as well as at least one polycarboxylic acid. The invention furthermore relates to the provision of a method for the production of the pigment preparation according to the invention. Finally, the invention relates to the use of the pigment preparation according to the invention in a flexographic ink.
2. Description of Related Art
The use, in an inkjet printing ink, of aluminum effect pigments produced by grinding is known from WO 2009/010288 A2. The d50 value lies in a range of from 1 to 15 μm. According to a preferred development, the average diameter, therefore the d50 value, of the particles lies in a range of from 2 to 5 μm. The average thickness of the aluminum effect pigments lies in a range of from 15 to 150 nm, preferably from 20 to 80 nm.
It has been shown that the average size distribution of the aluminum effect pigments known from WO 2009/010288 A2 is suitable in particular for use in inkjet printing inks.
Platelet-shaped aluminum pigments, with a narrow thickness distribution, which are at least partially covered with lubricant are known from WO 2008/077612 A2. The average thickness of the platelet-shaped aluminum pigments lies in a range of from 15 to 25 nm. Stearic acid, oleic acid or mixtures thereof are preferably used as lubricant.
In flexographic printing the printing ink is applied to an anilox roller from an ink tank via a fountain roller printing mechanism. Any excess printing ink is scraped off the anilox roller using a doctor blade. The anilox roller transfers the printing ink to a printing cylinder, which then applies the printing ink to the printing substrate guided via an impression cylinder. The printing ink collected from the ink tank is therefore transferred to two further rollers before the ink is printed onto the printing substrate. If printing inks containing metal effect pigments are used, during the transfer of the printing ink from the fountain roller to the anilox roller via the printing cylinder there is a decrease of metal effect pigments in the printing ink during every transfer of printing ink. As a result, the amount of metal effect pigments printed on the substrate to be printed on is insufficient (poor transfer behavior).
The metal pigments described in WO 2008/077612 A2 have a poor transfer behavior. In uses differing from flexographic printing, the aluminum effect pigments obtained by grinding according to the teaching of WO 2008/077612 A2 in contrast display optical properties which come very close to the pigments obtained by physical vapor deposition (PVD). The average size d50 of the pigments known from WO 2008/077612 A2 extremely preferably lies in a range of from 15 to 25 μm. These pigments are generally suitable for use in coatings, varnishes, printing inks, powder coatings, etc.
A metal effect pigment with additive is known from EP 2 128 204 A1, wherein the additive is at least partially applied to the metal effect pigment and comprises, as structural units, at least one carboxylic acid with at least four carbon atoms as well as at least one polyglycol ether, wherein the carboxylic acid and the polyglycol ether are covalently bonded to each other.
The additive is suitable in particular as lubricant in the production of metal effect pigments made of metal particles by grinding.
The metal effect pigments known from EP 2 128 204 A1 have an average size d50 in a range of from 1 to 200 μm, extremely preferably from 5 to 100 μm. The average thickness h50 lies in a range of from 15 nm to 5 μm, extremely preferably from 70 to 150 nm. The metal effect pigments are suitable in particular for use in printing inks.
WO 96/14347 A1 relates to a pigment dispersing additive present as copolymer. The copolymer comprises alternating units of a vinyl monomer and a diester of a dicarboxylic acid, wherein at least one ester group comprises a polyether group and wherein the copolymer has an acid value of less than 1.
WO 2009/156275 A1 relates to a pigment mixture with two different components, wherein one component is platelet-shaped graphite with an average particle size of less than 50 μm and a thickness of less than 100 nm, and wherein a further component is organic or inorganic pigment.
US 2004/0214927 A1 relates to a color concentrate composition for polymeric materials which contains at least one colorant, a compatible polymer, a wax binder and an agent for compounding.
WO 2004/024837 A1 relates to an aqueous pigment paste which is free from binders and friction resins and which contains at least one metal pigment, at least one thickener with non-associative action, at least one organic amine, at least one non-ionic surfactant as well as at least 50 wt.-% water.